In forklift type vehicle, the position of the shift lever is detected electrically, and the power shift transmission shifts in the forward and reverse manner by using the detected electrical signals. With reference to FIG. 9 which illustrates an oil pressure circuit of a known power shift transmission, when the driver changes the shift lever from the forward position to the reverse position, the power shift transmission detects the shift change by electrical signals, and the solenoid valves 1, 2 are controlled to move the shift valve 3. When the shift valve 3 moves, the supply of line pressure in the oil pressure circuit changes from the front clutch to the rear clutch 4, and the vehicle thus changes movement from the forward direction to the reverse direction.
When the shift lever is shifted into the neutral position, but the shift valve 3 sticks at the position where the shift valve 3 supplies oil pressure to the front clutch 5 and cuts off oil pressure to the rear clutch 4, oil pressure is supplied to the front clutch 5, regardless of the position of the shift lever.
In the situation where the shift valve 3 sticks at the position where the shift valve 3 cuts off oil pressure supplied to the front clutch 5 and supplies oil pressure to the rear clutch 4, oil pressure is supplied to the rear clutch 4 regardless of whether the shift lever is in the neutral position or the forward position. Therefore, in the situation where the shift valve 3 sticks in the manner mentioned above, oil pressure is supplied to a clutch opposite or different from the shift lever position.